Process for obtaining a composite article



United States Patent 3,462,827 PROCESS FOR OBTAINING A COMPOSITE ARTICLEJoseph Winter, New Haven, Conn., assignor to Olin Mathieson ChemicalCorporation, a corporation of Virginia No Drawing. Application Oct. 1,1965, Ser. No. 492,312, now Patent No. 3,381,366, dated May 7, 1968,which is a continuation-in-part of application Ser. No. 229,262, Oct. 2,1962. Divided and this application Nov. 29, 1967, Ser. No. 686,706

Int. Cl. B23k 31/02; B211) 3/00 US. Cl. 29-4723 8 Claims ABSTRACT OF THEDISCLOSURE This disclosure teaches a process for obtaining a compositearticle having a core of an aluminum base alloy cladwith a dissimilarmetal. The process is characterized by heating the core and rollingtogether the core and cladding at a speed of at least 25 feet per minutein one pass at the reduction between 35 and 80%, with the core andcladding coming together for the first time in the bite of the rolls.

This application is a division of US. patent application Ser. No.492,312, filed Oct. 1, 1965, now US. Patent 3,381,366 which in turn is acontinuation-in-part of U.S..

patent application Ser. No. 229,262, filled Oct. 2, 1962, now abandoned.

The present invention relates to composite metal articles. Moreparticularly, the present invention resides in composite metal articleshaving an aluminum core and to the processes whereby said articles areobtained.

Composite articles having an aluminum core and a dissimilar cladding arehighly desirable commercially due to the fact that the beneficialcharacteristics of the core and cladding materials may be obtained inone composite article. Ina single alloy frequently many propertiescannot be greatly modified by alloying or thermal treatments, forexample, such properties as modulus of elasticity, color, density, andstrength in combination with high thermal or electrical conductivity.However, by forming composites apparent properties of the cladding canbe generated while retaining the bulk properties of the core material.In this manner one can often obtain greatly modified and highlydesirable properties over the single alloy.

For example, aluminum has the advantage of high strength-to-weightratio, cold formability, low density and high conductivity. By formingaluminum composites one can retain these desirable properties whilegenerating properties of the cladding, such as wear resistance, color,oxidation resistance, high surface strength, chemical resistance,tarnish resistance, fine finishings, i.e., surface quality, etc.

Various uses to which composite aluminum articles may be put are asfollows: heat exchangers, electrical hardware, builders hardware,utensils, automotive components, shipping containers, ornamentalpurposes, and so forth.

However, the preparation of composite articles having an aluminum corepresents numerous practical problems. It has been difficult to produce asatisfactory composite article having an aluminum core due to thetendency of the cladding material to form a layer of brittle,intermetallic compounds at the interface of the aluminum core and thecladding. Aluminum is particularlydifiicult in this regard as it is avery potent compound former with a great variety of commercialmaterials. This layer may form at moderate temperatures or at elevatedtemperatures. The brittle layer of intermetallic compounds which soforms may shatter readily on flexing of the composite material, thusclearly limiting the utility of the composite.

Furthermore, the intermetallic compounds formed will thicken rapidly atelevated temperatures due to the rapid rate of diffusion common toaluminum in combination with most engineering materials. This thickintermetallic phase may tend to improve bonding between the twocomponents of the composite, but yields a weak link when the compositeis bent or flexed. In addition, the intermetallic compounds willdecrease the useable ductility of the composite.

In addition, with composite materials having an aluminum core, it isfrequently difiicult to obtain a well bonded composite which willwithstand normally expected use.

Aluminum in air is always coated with an adherent and/or flaky oxide.This oxide will produce an interference layer which inhibits bonding.Elevated temperatures increase the thickness of this oxide layer. Thisoxide layer frequently tends to break up on hot rolling but still canand often does cause severe problems.

One method of forming aluminum composites in order to overcome thesedifficulties is to form a partial bond by cold rolling followed bysubsequent diffusion anneals. This is an expensive process and thediffusion anneals tend to degrade the properties of the composite.

Another method is to eliminate oxygen completely from the compositeintersurface by, for example, evacuation and welding or treatment inenclosed, inert atmospheres. Another method is to provide bonding aidsof one type or another. Both of these methods are expensive andundesirable alternatives, and often unsatisfactory.

Accordingly, it is a principal object of the present invention toprovide new and improved composite articles having an aluminum core.

It is a further object of the present invention to provide convenientand expeditious processes whereby said composite articles are obtained.

It is a further object of the present invention to provide processes andarticles as aforesaid whereby the articles are characterized by havinghigh strengths, excellent physical properties and a wide variety ofuses.

It is a still further object of the present invention to provideprocesses and articles as aforesaid which overcome the numerouslimitations and disadvantages attendant upon the formation ofconventional composite articles having an aluminum core.

Still further objects and advantages of the present invention willappear from the ensuing discussion.

In accordance with the present invention, it has now been found that theforegoing objects and advantages may be readily obtained. The process ofthe present invention readily overcomes the disadvantages of the art andachieves a simple and convenient process for obtaining a highly usefulcomposite article clad on either one side or both sides and having acore of an aluminum base alloy clad with a dissimilar metal andpreferably a material selected from the group consisting of a dissimilaraluminum base alloy, a copper base alloy, a lead base alloy, a silverbase alloy, a nickel base alloy, a zirconium base alloy, a zinc basealloy, a chromium base alloy, a refractory metal, a titanium base alloy,a tin base alloy and an iron base alloy. The process of the presentinvention comprises: (A) providing said core in plate form in athickness less than /2 inch; (B) providing said cladding in plate formin a thickness less than 4 inch; (C) heating said core to a temperaturebetween 150 and 1,050 E; (D) rolling together said core and cladding ata speed of at least 25 and preferably 100 feet per minute in one pass ata reduction between 35 and 80%, with said core and cladding comingtogether for the first time in the bite of the rolls, said claddingcontacting the roll prior to contacting said core, with the includedangle between core and cladding upon entering the rolls being in excessof 5 degrees.

It is preferred to provide an angle between the cladding and core inexcess of upon entering the rolls in order to insure that the claddingand core will not come together earlier than in the bite of the rolls.Generally, the included angle between the core and cladding is between 5and 22.

It has been found that poor results are obtained if there is no includedangle between core and cladding upon entering the rolls or ifpre-contact between core and cladding is had prior to the bite of therolls.

In accordance with the present invention the cladding metal contacts theroll prior to contacting the core. On the front side of the rolls(entering side) the cladding and the rolls are travelling at differentlinear speeds; whereas, at the exit side they are going at the samespeed due to the reduction in thickness of the composite. The differencein travelling speeds between the cladding and the rolls coupled with thepre-contact between the cladding and the rolls generates a shearingstrain between the cladding and the rolls and introduces shearing at thebite of the rolls to the core-clad interface. This shearing strain inaddition to the normal shearing forces introduced by the rollingreduction at the core-clad interface results in turbulent flow of metalat the interface which causes more intimate bonding by increasing theinterfacial linear surface of the composite by 20% or more.

It has been found that the simple process delineated above achieves ahighly advantageous composite article, with the interface between thecore and cladding charac terized by the absence of atomic interdiffusionbetween base metal and cladding, with said interface being furthercharacterized by having at least 20% greater surface contact area thanplanar sheets.

The composite articles of the present invention are characterized byexcellent physical properties, very high bond strengths and the absenceof atomic interdiffusion between base metal and cladding, whichinterdiffusion may result in the formation of brittle compounds. Thepresent invention achieves these surprising advantages by means of asimple and convenient process and without the use of expensive devicessuch as are frequently employed in the art. In addition, the compositesof the present invention art not characterized by a thick brittle layerof intermetallics such as characterize conventional composites.

In accordance with the present invention any aluminum base alloy may beemployed as the core material, i.e., any alloy containing a majorproportion of aluminum. Typical alloys which may be employed include butare not limited to the following: high purity aluminum. aluminum alloys'l [00. 606], 3003, 3004, etc. 'lypical alloying substituents includebut are not limited to the following: magnesium,

.4 tin, copper, manganese, silicon, iron, chromium, zinc and so forth.

The aluminum base alloy core material should be provided in plate formhaving a thickness less than /2 inch, i.e., the core material may beprovided in strip, sheet or the like form. The core is always thethicker component of the composite.

It is preferred, but not required, in accordance with the presentinvention to mechanically roughen the bonding surfaces of both the coreand the cladding materials in order to assure good surface contact atthe bite of the rolls. For example, the surfaces may be wire brushed orabraded, etc.

The cladding material may be any of the cladding materials indicatedhereinabove. The cladding may be, for example, any of the foregoingaluminum base alloys, providing that the cladding material is dissimilarto the core materal. By dissimilar aluminum alloy or dissimilar metal,the present invention contemplates, inter 'alia, both an aluminum alloyhaving different alloying ingredients or the same alloy with differentphysical characteristics.

' The optimum cladding materials are iron base alloys and copper basealloys.

In addition, any copper, lead, zirconium, tin, nickel, zinc, chromium,cobalt, silver, titanium or iron alloy may preferably be employed as thecladding material. High purity copper tin, lead, zirconium, nickel,zinc, chromium, refractory metal, titanium, silver or iron or basealloys of these materials may be readily employed.

Typical alloying substituents which may be employed include, but are notlimited to, the following: with copper one may alloy zinc, tin,aluminum, phosphorus, iron and lead; with lead one may alloy tin,arsenic and cadmium; with tin one may alloy arsenic, cadmium, copper,lead and antimony; with nickel one may alloy chromium, iron, copper,titanium, aluminum, vanadium, tungsten, and cobalt; with zinc one mayalloy copper, iron, aluminum and magnesium; with silver one may alloycopper and nickel; with iron one may alloy carbon, aluminum, titanium,zinc, lead, silicon, phosphorus, sulfur, nickel and chromium; and soforth. By refractory metals are ineluded molybdenum, vanadium, tantalum,columbium and base alloys thereof.

The cladding material should be in plate form less than /1 inch inthickness, i.e., the cladding and the core material should be in wroughtform, for example, coils of strip, sheet, etc.

After bonding the resultant composite has a thickness less than 0.75inch where the aluminum is clad on two sides and less than 0.52 inchwhere it is clad on one side. The lowest gage materials, both core andcladding, which can be conveniently worked with, is on the order of0.001 inch.

The starting materials, both core and cladding, can be in any temper orcondition, hard or soft. Surface oxides are generally no handicap to theprocess of the present invention. This is quite surprising and is asignificant advantage of the present invention since conventionalprocessing must remove surface oxides prior to the formation of thecomposite. In fact, conventional processing frequently forms compositesin special atmospheres so that one cannot form surface oxides prior tothe formation of the composite. These special precautions are notrequired in the present invention.

It is, however, highly desirable to remove dirt or adhering lubricantfrom the surface of the metal prior to the process of the presentinvention in order to assure good contact between the core and thecladding materials. Any conventional cleaning processes may be readilyemployed, for example, the core and cladding materials may be passedthrough a soap or a detergent solution in accordance with conventionalprocedures. Examples of such cleaning procedures include the use ofcommercial alkaline cleaners and solvent cleaners, such as carbontetrachloride and trichloroethylene.

It should be noted that it is a particular advantage of the presentinvention that it is unnecessary to utilize bonding aids, such as a thincoating of a dissimilar metal, in order to effect the strongly adherentcladding of the present invention.

The core material is then heated to a temperature between 150 and 1,050F., and preferably to a temperature between 550 and 950 F. It isimportant to note that the cladding material is not heated but is leftin the cold form.

The rolling step of the present invention is particularly critical. Thecore and cladding materials enter the rolls with the core material beingprovided at a temperature between 150 and 1050 F. and preferably between550 and 950 F. The core and cladding enter the rolls at an angle so thatthey come together for the first time in the bite of the rolls. Thematerials are rolled at a high speed of at least 25 feet per minute andpreferably at least 100 feet per minute, in one pass, with a reductionbetween 35 and 80% and preferably between 40 and 70%. Naturally, at thelower rolling speeds greater reduction is required. It is preferred thatthe core and cladding enter the rolls at an angle in excess of andgenerally at an included angle of between 5 and 22 in order to assurethat the core and cladding will not come together earlier than at thebite of the rolls and in order to put as much shear as possible at theinterface. The shear at the interface enables the provision of at least20% increased surface area than between the planar materials, i.e., theinterface between the core and cladding is characterized by a wave-likeformation with a significant increased interfacial contact area. It isfurther noted that the interfacial surface between the core and claddingis characterized by the absence of interatomic diffusion between thecore and cladding material. For example, when a copper alloy cladding isused, there is substantially no diffusion of copper atoms into thealuminum core.

Further in accordance with the present invention the cladding metalcontacts the roll before contacting the core metal. This is true whetherthe core is to be clad on one side or both sides.

In general, the core material should come into the rolls substantiallyhorizontally, particularly where the core is to be clad on both sides.

Naturally, the present invention contemplates cladding the aluminum coreon both sides with dissimilar metals on each side.

A further advantage of the present invention is that subsequent to therolling operation the composites of the present invention do not requiresubsequent diffusion anneals, i.e., conventional processing frequentlyrequires diffusion anneals to secure the bond between core and cladding.The fact that the present invention does not require diffusion annealsis particularly significant since diffusion anneals might and frequentlydo cause blisters or the like due to the long treatment times requiredand codiffusion of gases to the interface between the core and cladding.

In fact, subsequent to the rolling operation no further operationswhatever are required. The composites of the present invention areprovided in commercial form ready to be used for the desiredapplication. It may naturally be desirable to perform conventionalsubsequent operations for particular applications. For example, shortthermal treatments for stress relief or the attainment of desiredproperties, e.g., a short heat treating anneal or aging treatment, arolling operation for dimensional control, additional work hardening,and so forth.

The present invention will be more readily understandable from aconsideration of the following illustrative examples.

Example 1 The following is a detailed description of the generalprocedures used in the specific examples which follow. Except whereotherwise set out in the specific examples,

the general manipulative operations described here are those used inpreparing and bonding the specimens of the specific examples.

A strip of base sheet metal, as for example, a strip of aluminum metalof 6 inches in length, 4 inches in width, and having a thickness of0.125 inch, was first cleaned preparatory to joining. The cleaning stepsincluded a wet chemical cleaning treatment such as a degreasing of themetal surface, as by immersion in a degreasing solvent such astrichloroethylene, or in an inhibited solution of an alkaline cleaningagent such as a solution of trisodium phosphate in water at 160 F.Following such a wet chemical cleaning treatment, the surface to beunited was rinsed in flowing cold tap water.

After a wet chemical cleaning treatment, the surfaces to be joined maybe mechanically cleaned and roughened by mechanical wire brushing, aswith a cleaned stainless steel rotary wire brush, prior to beingsubjected to any thermal treatment.

A strip of a cladding metal, such as stainless steel, having a widthapproximately corresponding to those of the aluminum strip but having alength perhaps 20 percent greater than that of the base metal and athickness of approximately one-fiftieth to one-tenth of the aluminumbase, was cleaned in a manner such as that described for the aluminumabove.

The cladding strip was then folded at one end to form a clip which wouldreceive the lead edge of the aluminum strip for introduction into thenip of the rolls of a rolling mill. The cladding strip was also bent inthe form of an arc resting at its ends on the base sheet but suspendedalong its length out of thermal and physical contact with the base, withthe angle between the cladding and the core upon entering the rollsbeing between l020 and with the cladding contacting the rolls prior tocontacting the core. The 20% increase in starting length of the claddingwas incorporated to insure the retention of an arc during the entirerolling process.

After preparing the cladding and base 'metal parts in this way, the basemetal only was heated at a temperature, and for a time, to impart thedesirable heat to the base. Immediately after removal of the base from aheat supply means, such as a furnace, the cladding strip is clipped onto the lead end of the hot base metal strip and the assembly isimmediately inserted into the nip of the rolls with the speed of therolls being between and feet per minute. As the assembly is drawnrapidly between the rolls the clad metal is driven forcefully intophysical and thermal contact with the heated base metal in the bite ofthe rolls without pre-contact.

In all cases unless indicated to the contrary, a firmly bonded compositewas obtained characterized as follows: (1) as shown by microscopicexamination there was no interatomie diffusion between the cladding andbase metal, and (2) as shown by microscopic examination there was atleast 25% greater bonding area at the interface than with the planarmaterials with the interface being characterized by a wave-likeformation.

Example 2 A specimen of austenitic stainless steel (188 type) foil wasclad onto a base strip of aluminum alloy 6061 as described in Example 1.

The wet chemical cleaning procedure of Example 1 was followed exceptthat the surfaces to be confronted were cleaned by degr-easing intrichlorethylene only. This was followed by a wire brush cleaning ofboth of the surfaces to be confronted in joining. The cladding strip wasbent to have a flat lead edge lying parallel to the base sheet and anarched 'rnidsection between the ends of the cladding strip in contactwith the base.

The aluminum substrate only was heated to 750 F. for twenty minutes.Immediately after withdrawal from the furnace the stainless strip wasplaced on the aluminum base sheet in the manner of Example 1 and theassembly was introduced by its lead edge into the nip of rapidlyrotating rolls, each having a diameter of about ten inches. The rollswere set at a clearance to provide a reduction of the assembly thicknessof about 50 percent in this single pass through the rolls. The assemblywas bonded in passing through the nip of the rolls at about 150 feet perminute.

Two more assemblies of 6061 aluminum base metal and 18-8 type stainlesscladding metal were prepared for bonding by a procedure preciselyduplicating that described above except for the clearance settingbetween the rolls. For one of these assemblies the rolls were set toreduce the thickness by 65 percent. For the other assembly the rollswere set for a reduction of percent.

The results of these separate bonding operations were as follows:

After rolling the sample to be reduced by 50 percent showed very slightedge cracking along both sides of the cladding layer. The stainlesssteel and aluminum were not bonded at the lead end where the flatportion of the stainless steel rested on the hot aluminum substrate, butan excellent bond was found in along the length of the specimen.

Excellent bonding was also found between the substrate and cladding ofthe specimen to be reduced 65 percent. It was observed, however, thatthe gage of the stainless steel was reduced from about .005 inch toabout .002 inch. Severe transverse ruptures had developed in the body ofthe cladding.

The specimen to be reduced 25 percent showed the surface rougheningwhich results from the application of bonding energy but did not resultin significant bond formation.

Example 3 A composite specimen was prepared by bonding a base strip ofaluminum alloy 1100 to a cladding strip of an austenitio 18-8 stainlesssteel (type 302) substantially as described in Example 1.

Before bonding the aluminum was about .070 inch thick and the stainlesswas .005 inch thick. The metal surfaces were washed withtrichlorethylene and wire brushed on the surfaces to be confronted injoining. The aluminum was heated to 950 F. The strips were rapidlyassembled and rapidly bonded in the manner of Example 1 with the spacingbetween the rolls set to produce a stainless clad aluminum composite of0.040 inch in thickness. Rolling speed was about 150 feet per minute.Satisfactory bonding was found to have been produced over about 75percent of the stainless steel specimen, the areas of such bonding beingfound to be distributed in a random pattern.

A sample 3.5 inches square was cut from a well bonded region of thecomposite specimen and cupped in a standard double acting deep drawingcupping press equipped to first punch a circular blank having a3.11-inch diameter, and to then deep draw the blank to produce a cuphaving a 1.125-inch diameter and having side walls approximately 1.2inches high. The cup formed successfully from the blank with thestainless steel on the outside. The base of the cup thus formed wasfound to have the unified structure of the bonded sheet but thestainless in the sidewall of the cup was ruptured by shearing, althoughthe aluminum base was not ruptured. The bond between the stainless steeland aluminum was good and this was confirmed by metallographicexamination.

Example 4 The procedure of Example 3 was repeated with the exceptionthat in this case there was utilized a base metal specimen of aluminumalloy 6061 and a cladding metal strip of type 302 stainless steel.

The bond which formed extended over about 95 percent of the compositespecimen. Some edge cracking and folding were produced evidently due tomisalignment of the stainless steel cladding metal on the aluminumsubstrate as the assembly entered the roll nip.

Example 5 The procedure of Example 3 was again repeated with theexception in the case being that the specimens were a one-inch wide hardrolled strip of zircaloy and a wider base of aluminum alloy 1100.

An extremely strong overall bond was produced between the zircaloy andaluminum strips. Significant transverse fracturing of the zircaloyoccurred in the head end, i.e., the end which first underwent rolling,where greater deformation occurred in the zircaloy. At the tail end,where the zircaloy strip was impressed into the softer aluminum basemetal, less deformation to the zircaloy occurred during the bondingalthough uniform coherent cladding occurred.

Example 6 Three base metal strips of aluminum alloy 3003 each having athickness of 0.125 inch, and three cladding strips of stainless steeleach having a thickness of .005 inch, were prepared as described inExample 2.

The aluminum specimens were each heated to 950 F. instead of to 1,000 F.and, immediately after removal of the aluminum from the furnace, therespective specimens of stainless steel and aluminum were assembled andbonded at a rolling speed of 50 feet per minute. The rolls were set toreduce each of the assemblies by rolling by 50 percent as taught inExample 2.

No bonding or light sticking as by mechanical interlocking whatsoeverwas produced. The aluminum intersurface which had contacted thestainless steel in rolling had the appearance of having been lightlyburnished as a result of the low speed procedure.

The duplication of the procedure of Example 2 but at the lower rollingspeed and slightly lower substrate preheat temperature established thesignificance of rolling speed in the development of good bonding andthat at lower rolling speeds greater reduction is required. For example,the procedure of the foregoing example was repeated except that thereduction was and good bonding resulted.

Example 7 Two composite sheets were prepared as described in Example 2,one of type 302 stainless steel on an aluminum alloy 6061 base and theother type 302 stainless steel on a. 3003 alloy base. The rolls were setto provide a reduction of 40 percent and to provide a final gage of0.040 for the composite.

The products formed were well bonded composite sheets.

Example 8 Two assemblies were prepared for bonding by degreasing andwire brushing the surfaces to be confronted as described in Example 1.The two cladding strips were specimens of cold rolled cupro-nickelhaving a thickness of 0.005 inch and the two base strip specimens wereannealed aluminum alloy 1100 having a thickness of 0.107 inch. Thecupro-nickel composition of the cladding strips was commercial alloyhaving approximately 18 percent nickel by weight and the balance copper.

A first assembly of strips was prepared for hot rolling by riveting theedges thereof together and heat-ing the riveted assembly to 950 F. inpreparation for cladding.

The second assembly was prepared for rolling by heating only thealuminum to a temperature of 950 F. This second assembly was rolled inaccordance with the procedure of the present invention.

Both assemblies were reduced by rolling with the rolls set to give areduction of approximately 50 percent.

The first assembly produced a composite product in which the claddinghad substantially greater discoloration of the external surface of thecladding than that produced on the second assembly. Also the degree ofadhesion of the cladding to the substrate was substantially greater andmore uniform in the second assembly than in the first.

Example 9 A cladding metal strip of commercial purity titanium having athickness of about 0.002 inch and a strip of aluminum alloy 3004 havinga thickness of 0.040 inch were prepared for bonding as described inExample 1 except that the wire brushing was performed on the surface ofthe aluminum strip only. The aluminum strip was heated to 950 F. andbonded to the titanium strip using care to minimize thermal contactbetween the strips. The assembly was bonded with the clearance betweenthe rolls set to give a reduction in thickness of the assembly of 50percent.

A strong bond was formed between the two strips and the surface claddingdisplayed surface rupture in the wave form closely resembling the arrayof waves on the exposed surface of a large body of water over which airis moving at a relatively low velocity.

Example Several specimens of aluminum having a thickness of about 0.040were prepared for bonding as described in Example 1. Several specimensof high purity silver hav ing a thickness of 0.001 inch were alsoprepared for bonding by solvent degreasing as described in Example 1.

In this example, the sample of aluminum was an aluminum base alloycontaining a small percentage of tin as described in United StatesPatent 3,186,836.

Each of the aluminum specimens Was heated in an oven maintained at atemperature of about 700 F. for a period of about 10 to minutes. Thealuminum was removed from the furnace and the silver was bonded theretoemploying a rolling speed of about 200 feet per minute following theprocedure set out in Example 2.

In bonding the clearance between the rolls was set to give a reductionof approximately 50%. The measured final gage of the composite specimenwas between 0.022 and- 0.024 inch. A piece of the silver cladding whichwas bonded to the aluminum was removed by mechanical stripping and itsthickness measured. The thickness of this silver cladding was found tobe approximately /2 of 1 mil.

Example 11 The procedure of Example 10 was again duplicated with theexception that in this case 0.002 inch copper was used in place of the0.001 inch silver, the copper in this case being chemical grade foil,meaning that the copper was of approximately 0.9999% copper purity orhigher.

Prior to bonding the copper specimen was cleaned by pickling in asolution of approximately 25% HNO in Water. The aluminum sample wasprepared also as described in Example 10 with surface wire brushing andsolvent degreasing, but was not etched. The copper sample was neitherwire brushed nor solvent degreased.

A series of 5 different rolling reductions was carried out. Beforerolling each of the aluminum specimens was about 2 inches wide by 5inches long and had a thick ness of 0.040 inch appoximately.

A series of 5 different rolling reductions were performed with the rollsset at values to give reductions of the assemblies ranging from about toabout 65% with 3 intermediate values, at approximately equal percentageincrements.

The sample bonded at approximately 20% reduction was very weakly bondedand exhibited edge peeling.

An optimum bonding was found at reduction values of betweenapproximately 30 and 40%.

At reductions of approximately 50% and above transverse fracturing wasobserved in the thin copper cladding and the fracturing increased at thehigher reduction percentage.

It was possible to reduce this copper thickness to an approximatelytransparent thickness where the silvery appearance of the aluminumbeganto become apparent through the copper deposits formed on itssurface by this bonding.

This invention may be embodided in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefor to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

1. A process for obtaining a composite article having a core-selectedfrom the group consisting of aluminum and aluminum base alloys clad witha dissimilar metal selected from the group consisting of iron and ironbase alloys which comprises:

(A) providing said core in plate form in a thickness less than /2 inch;

(B) providing said cladding in plate form in a thickness less than inch;

(C). heatingsaid core only to a temperature between 150and1050 F.;

(D) rolling together said core and cladding at a speed of at least 25feet per minute in one pass at a reduction between 35 and with said coreand cladding coming together for the first time in the bite of therolls, said cladding contacting the roll prior to contacting the core,with the included angle between core and cladding upon entering therolls being in excess of 5 degrees, wherein said core and cladding arerolled together in direct metalto-metal contacting relationshipthroughout the confronting surfaces thereof;

(E) wherein said processing is conducted under atmospheric conditions,

thereby forming an integrated composite article.

2. A process for obtaining a composite article having a core selectedfrom the group consisting of aluminum and aluminum base alloys clad witha dissimilar metal selected from the group consisting of iron and ironbase alloys which comprises:

(A) providing said core in plate form in a thickness less than inch; (B)providing said cladding in plate form in a thickness less than A inch;

(C) heating said core only to a temperature between 550 F. and-1050 F.;

(D) rolling together said core and cladding at a speed of at least feetper minute in one pass at a reduction between 35 and 80%, with said coreand cladding coming together for the first time in the bite of therolls, said cladding contacting the roll prior 'to contacting the core,with the included angle between core and cladding upon entering therolls being between 5 and 22 degrees, wherein said core and cladding arerolled together in direct metalto-metal contacting relationshipthorughout the confronting surfaces thereof;

(E) wherein said processing is conducted under atmospheric condition,

thereby forming an integrated composite article.

3. A process according to claim 2 wherein said included angle is inexcess of 10.

4. A process according to claim 2 wherein said core enters the rollssubstantially horizontally.

5. A process according to claim 2 wherein said core and cladding arerolled together in one pass at a reduction between 40 and 70%.

6. A process according to claim 2 wherein the surfaces of said core andcladding to be bonded are mechanically roughened prior to rolling.

7. A process according to claim 2 wherein said core is clad on bothsides.

8. A process according to claim 2 wherein said core and cladding arecleaned prior to rolling.

- References Cited UNITED STATES PATENTS Jordan 29-470.1 Boessenkool29-497.5 Mushovic 29-4975 Mushovic 29-4975 -X Dulin 29-488 Jost. 1

Fulford 29-4975 X Wardlaw 29-4975 X Ulam 29-488 Smith 29-471.1

Avellone 29-4975 Fisher et a1.

JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner US.Cl. X.R.

